1. Field of the Invention
The invention is radial piston engines;
2. Description of the Prior Art
A radial piston pump of this kind has been disclosed in DE 23 38 489 B2. In this known pump the suction valve has a shaft which leads from its closing body equaxially to the pump piston and supports the valve closing spring outside the cylinder chamber. This valve closing spring engages the shaft at one end and indirectly engages the pump housing at the other end. When the suction valve opens, the closing force of the spring therefore increases along with the stroke.
Radial piston pumps of this kind, which have a number of pump pistons (pump elements), must meet strict requirements with regard to uniform delivery: with a low supply quantity, all of the pump elements should be feeding and variation between the supply quantities of the individual pump elements should remain within strict limits. At a low pressure of the fuel supplied to the radial piston pump, difficulties in meeting these requirements arise, even with low opening pressure differences between the suction valves of the pump elements.
In the crown piston pump mentioned, the opening process of the suction valve should be assisted by virtue of the fact that the closing body of the valve disposed in the cylinder chamber, at the top dead center of the pump piston is largely encompassed by the pump piston and as a result, the piston exerts an aspirating action on the closing body during the intake stroke.
The radial piston pump according to the invention, has the advantage over the prior art that the opening of the suction valve is assisted at a low pressure of the supplied fuel by virtue of the fact that the closing force of the valve closing spring decreases as the intake stroke of the pump piston increases. In a multi-piston pump, an opening of all of the suction valves is thus reliably achieved and a relatively high degree of delivery uniformity is produced. As a result, an opening pressure adjustment of the suction valves can be eliminated or can be carried out with reduced precision.
DE 44 06 803 A1 has in fact disclosed a radial piston pump with a pump piston that is flowed through axially, in which a suction valve is disposed, whose valve closing spring engages the closing body of the suction valve at one end and engages the pump piston at the other end. When the suction valve opens, however, the closing force of the spring, increases along with the stroke.
Another feature of the invention permits the size of the radial piston pump to be reduced since the valve closing spring is disposed essentially inside the structural volume of the pump piston. This disposition simultaneously achieves a guidance of the valve closing spring.
Another feature enables sufficient guidance of the closing body shaft to be likewise achieved while simultaneously reducing the dead volume of the pump.
In a modification of the invention, direct introduction of the spring force into the components is used to control the valve. As a result, only the dimensional deviations of a few components affect the adjustment of the suction valve.
Other features and advantages of the invention will be apparent from the detailed description contained below, taken with the drawings, in which:
FIG. 1 is a sectional view of a radial piston pump and
FIG. 2 shows an enlarged detail II from FIG. 1 of a suction valve of the pump.